From Wikipedia:

Those who possess a doctoral degree are generally entitled to call themselves "Doctor", although restrictions apply in some jurisdictions. Outside academia, the use of the term "doctor" as a form of address is usually limited to certain health professionals with doctoral degrees. For example medical doctors (physicians) usually use the title "Doctor" as a prefix. Dentists, podiatrists, chiropractors, osteopaths, optometrists and veterinarians are also called Doctor whether or not they possess a doctoral degree.

From a wedding invitation etiquette site:

My father has a Ph.D. does he use "Doctor" on my wedding invitations?

Ph.D. is an academic title that is used only in academic settings. The use of "Doctor" on wedding invitations is reserved for medical doctors and ministers with advanced degrees

Sophia, it seemed to vary from prof to prof at my college. I tried to remember how the instructor introduced himself, and use that. I don't get the feeling that most of the comments using "prof" are from his own students (ita, he is also a prof) but I could be wrong about that. It's handy to know, either way. It's just one of a billion factoids my brain has rid itself of, over the past 10 years.

Parenting makes me stupid. By the time life permits me to return to the work force, my best chance at gainful employment is going to involve a lot of hoping that shoe-tying will be a near-forgotten art, suddenly in great demand.

Well, I went and fixed one of the problems they were whining to me about. That only means they're going to keep coming back to me with more problems.

Why do the smelly people always come sit next to me?

Well, I went and fixed one of the problems they were whining to me about. That only means they're going to keep coming back to me with more problems.

Yes, fixing stuff only encourages them....

although restrictions apply in some jurisdictions

This makes no sense.

Why not call a PhD doctor? My understanding is that it's the reverse in Great Britain.

Finally, 5 percent of those taking part in the survey believed that all that was needed to beat the Big C was a positive attitude.

They'll have to let us know how that works out for them if they should ever develop cancer themselves. Via seance, most likely.

90 percent of the people who have had cancer want to beat that 5 percent into a bloody pulp.

Wroddy FitzWrod of Wroddenton, on Loch McWrod.

I'm at an institute with loads of scientists. I call everyone Doctor Whatever unless told to do otherwise, because odds are good that they have either a PhD or an MD. I have neither, for what it's worth.

Well, I went and fixed one of the problems they were whining to me about. That only means they're going to keep coming back to me with more problems.

This is why I strive to be as inefficient as possible at all times. If I don't fix the problems I have now, how can I possibly be trusted with any more?

Why not call a PhD doctor?

Why not contravene any of the titling etiquette? It's not like logic can be applied.

I don't see any reason to bother, so I don't and won't. Others differ.

My sister didn't go by Dr. socially when she was living in the UK last, and I'm pretty sure my mother didn't socially when she worked there either.